Comparison of Four-Dimensional Magnetic Resonance Imaging Analysis of Left Ventricular Fluid Dynamics and Energetics in Ischemic and Restrictive Cardiomyopathies.

BACKGROUND: Time-resolved three-directional velocity-encoded (4D flow) magnetic resonance imaging (MRI) enables the quantification of left ventricular (LV) intracavitary fluid dynamics and energetics, providing mechanistic insight into LV dysfunctions. Before becoming a support to diagnosis and patient stratification, this analysis should prove capable of discriminating between clearly different LV derangements. PURPOSE: To investigate the potential of 4D flow in identifying fluid dynamic and energetics derangements in ischemic and restrictive LV cardiomyopathies. STUDY TYPE: Prospective observational study. POPULATION: Ten patients with post-ischemic cardiomyopathy (ICM), 10 patients with cardiac light-chain cardiac amyloidosis (AL-CA), and 10 healthy controls were included. FIELD STRENGTH/SEQUENCE: 1.5 T/balanced steady-state free precession cine and 4D flow sequences. ASSESSMENT: Flow was divided into four components: direct flow (DF), retained inflow, delayed ejection flow, and residual volume (RV). Demographics, LV morphology, flow components, global and regional energetics (volume-normalized kinetic energy [KEV ] and viscous energy loss [ELV ]), and pressure-derived hemodynamic force (HDF) were compared between the three groups. STATISTICAL TESTS: Intergroup differences in flow components were tested by one-way analysis of variance (ANOVA); differences in energetic variables and peak HDF were tested by two-way ANOVA. A P-value of <0.05 was considered significant. RESULTS: ICM patients exhibited the following statistically significant alterations vs. controls: reduced KEV , mostly in the basal region, in systole (-44%) and in diastole (-37%); altered flow components, with reduced DF (-33%) and increased RV (+26%); and reduced basal-apical HDF component on average by 63% at peak systole. AL-CA patients exhibited the following alterations vs. controls: significantly reduced KEV at the E-wave peak in the basal segment (-34%); albeit nonstatistically significant, increased peaks and altered time-course of the HDF basal-apical component in diastole and slightly reduced HDF components in systole. DATA CONCLUSION: The analysis of multiple 4D flow-derived parameters highlighted fluid dynamic alterations associated with systolic and diastolic dysfunctions in ICM and AL-CA patients, respectively. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 3.

4D flow evaluation of blood non-Newtonian behavior in left ventricle flow analysis.

Blood is generally modeled as a Newtonian fluid, assuming a standard and constant viscosity; however, this assumption may not hold for the highly pulsatile and recirculating intracavitary flow in the left ventricle (LV), hampering the quantification of fluid dynamic indices of potential clinical relevance. Herein, we investigated the effect of three viscosity models on the patient-specific quantification of LV blood energetics, namely on viscous energy loss (EL), from 4D Flow magnetic resonance imaging: I) Newtonian with standard viscosity (3.7 cP), II) Newtonian with subject-specific hematocrit-dependent viscosity, III) non-Newtonian accounting for the effect of hematocrit and shear rate. Analyses were performed on 5 controls and 5 patients with cardiac light-chain amyloidosis. In Model II, viscosity ranged between 3.0 (-19%) and 4.3 cP (+16%), mildly deviating from the standard value. In the non-Newtonian model, this effect was emphasized: viscosity ranged from 3.2 to 6.0 cP, deviating maximally from the standard value in low shear rate (i.e., <100 s-1) regions. This effect reflected on EL quantifications: in particular, as compared to Model I, Model III yielded markedly higher EL values (up to +40%) or markedly lower (down to -21%) for subjects with hematocrit higher than 39.5% and lower than 30%, respectively. Accounting for non-Newtonian blood behavior on a patient-specific basis may enhance the accuracy of intracardiac energetics assessment by 4D Flow, which may be explored as non-invasive index to discriminate between healthy and pathologic LV.

Accelerated Clustered Sparse Acquisition to Improve Functional MRI for Mapping Language Functions.

BACKGROUND: Functional magnetic resonance imaging (fMRI) is a useful method for noninvasive presurgical functional mapping. However, the scanner environment is inherently unsuitable for the examination of auditory and language functions, due to the loud acoustic noise produced by the scanner. Interleaved acquisition methods alleviate this problem by providing a silent period for stimulus presentation and/or response control (sparse sampling) but at the expense of a diminished amount of data collected. There are possible improvements to these sparse acquisition methods that increase the amount of data by acquiring several images per event (clustered sampling). We tested accelerated clustered fMRI acquisition in comparison with conventional sparse sampling in a pilot study. METHODS: The clustered and sparse acquisition techniques (7.4 minutes scanning time per protocol) were directly compared in 15 healthy subjects (8 men; mean age: 24 ± 3 years) using both a motor (tongue movement) and a language (overt picture-naming) task. Functional imaging data were analyzed using Statistical Parametric Mapping software (SPM12 Wellcome Department of Imaging Neuroscience, London, UK). For both tasks, activation levels were compared and Euclidean distances (EDs) between cluster centers (i.e., local activation maxima and centers of gravity) were calculated. Overlaps and laterality indices were computed for the picture-naming task. In addition, the feasibility of the clustered acquisition protocol in a clinical setting was assessed in one pilot patient. RESULTS: For both tasks, activation levels were higher using the clustered acquisition protocol, reflected by bigger cluster sizes (p < 0.05). Mean ED between cluster centers ranged between 9.9 ± 5.4 mm (left superior temporal gyrus; centers of gravity) and 16.6 ± 13.2 mm (left inferior frontal gyrus; local activation maxima) for the picture-naming task. Overlaps between sparse and clustered acquisition reached 88% (Simpson overlap coefficient). A similar activation pattern for both acquisition methods was also confirmed in the clinical case. CONCLUSION: Despite some drawbacks inherent to the acquisition technique, the clustered sparse sampling protocol showed increased sensitivity for activation in language-related cortical regions with short scanning times. Such scanning techniques may be particularly advantageous for investigating patients with contraindications for long scans (e.g., reduced attention span).

Evaluation of 3.0-T MRI Brain Signal after Exposure to Gadoterate Meglumine in Women with High Breast Cancer Risk and Screening Breast MRI.

Background Otherwise healthy women at high risk for breast cancer undergo annual contrast agent-enhanced breast MRI screening examinations, resulting in high cumulative doses of gadolinium-based contrast agents (GBCAs). Whereas the majority of studies showed no T1 signal ratio increase in deep brain nuclei after more than six doses of macrocyclic GBCA, this has not been explored in a healthy study population. Purpose To assess whether women who are administered large cumulative doses of macrocyclic GBCA with breast MRI at high-risk breast cancer screening exhibit T1 alterations in deep brain nuclei. Materials and Methods In this prospective study from November 2017 to March 2018, healthy women who were either exposed (because of high-risk breast cancer screening) or unexposed to only gadoterate meglumine underwent 3.0-T brain MRI with a dedicated head coil, including T1 mapping and magnetization-prepared rapid gradient-echo sequences. T1 times and T1 signal intensities were measured in the dentate nucleus (DN), globus pallidus (GP), crus anterior of capsula interna (CA), and pons. Ratios of DN to pons and GP to CA were calculated, and univariable Pearson correlation coefficients were calculated. Multivariable analysis included partial regression analysis. Results This study evaluated 25 women (mean age, 51 years ± 11 [standard deviation]) who were exposed to a mean GBCA dose of 129 mL (median 112 mL; range, 70-302 mL) and 16 women (mean age, 37 years ± 10) who were never exposed to any GBCA. Infratentorially, no correlation between cumulative GBCA dose and T1 times or signal intensity ratios was detected (P = .66 and .55, respectively). In partial correlation analysis by considering age as a confounder, there was a moderate negative correlation between GP-to-CA ratio and GBCA dose (r = -0.40; P = .01) but not for GP T1 times (r = 0.19; P = .24). Conclusion After administration of relatively large cumulative doses of gadoterate dimeglumine, healthy women at high risk for breast cancer who underwent annual contrast-enhanced breast MRI screening did not exhibit T1 signal increase in deep brain nuclei at 3.0-T MRI. © RSNA, 2019.

A new imaging method for assessment of aortic dissection using four-dimensional phase contrast magnetic resonance imaging.

INTRODUCTION: Medical management of type B aortic dissection can result in progressive dilation of the false lumen and poor long-term outcome. Recent studies using models of aortic dissection have suggested flow characteristics, such as stroke volume, velocity, and helicity, are related to aortic expansion. The aim of this study was to assess whether four-dimensional phase-contrast magnetic resonance imaging (4D PC-MRI) can accurately visualize and quantify flow characteristics in patients with aortic dissection and whether these features are related to the rate of aortic expansion. METHODS: Twelve consecutive patients with medically treated type B thoracic aortic dissection underwent a three-dimensional (3D) MRI anatomy scan using a blood pool contrast agent. Two-dimensional phase contrast MRI data (2D PC-MRI) were acquired in the ascending and descending aorta and 4D PC-MRI data were acquired in the entire thoracic aorta. The 2D PC-MRI measurements were used to assess the quality of the 4D PC-MRI velocity data. Stroke volume, velocity, and the direction of flow were calculated using 4D PC-MRI and related to the rate of aortic expansion measured on contrast-enhanced computed tomography. RESULTS: Comparison of 2D PC-MRI and 4D PC-MRI measurements showed good correlation (Pearson R(2) = 0.98; 95% confidence interval [CI], 0.9818-0.9953; P < .0001) and no proportional bias (bias = 1.0 mL; standard deviation, 4.6). The median aortic growth rate was 6.1 mm/y (interquartile range [IQR], 1.1-15.1 mm/y), and this correlated well with the growth rate of the false lumen (Spearman ρ = 0.62; 95% CI, 0.06-0.89; P = .0347). False lumen thrombosis (FLT) was seen in 7 of 12 patients and was not associated with reduced aortic expansion rate (FLT present: 11.4 mm/y; IQR, 3.6-21.4) vs FLT absent: 9.9 mm/y; IQR, 3.4-24.2; Mann-Whitney P = .8763). False lumen stroke volume and velocity were associated with more rapid aortic expansion (ρ = 0.80 [95% CI, 0.39-0.94; P = .0029] and ρ = 0.59 [95% CI, 0.09-0.87; P = .0480] respectively). The position of the dominant entry tear was associated with rapid expansion, which tended to be higher with distal vs proximal entry tears (distal, 21.4 mm/y [IQR, 11.4-48.9] vs proximal, 5.5 mm/y [IQR, 3.4-16.6]; Mann-Whitney P = .096). Helical flow was seen in the false lumen in 8 of 12 patients and was related to the rate of aortic expansion (ρ = 0.83, P = .0154). CONCLUSIONS: 4D PC-MRI can be accurately applied to visualize and quantify flow characteristics in patients with aortic dissection. Stroke volume, velocity, distal dominant entry tears, and helical flow are related to the rate of aortic expansion. This study demonstrates the potential of this new imaging method. A larger prospective study is now required to measure flow characteristics and determine their predictive value for risk stratification of patients with aortic dissection.